The present invention relates to an automatic document feeder which is adopted in an image reading apparatus such as a copy machine or facsimile machine.
In a conventional automatic document feeder such as disposed on a copy machine body, there has been generally adopted such a constitution that the documents placed on a document tray are automatically fed and conveyed sheet by sheet toward reading means on the copy machine body, and the fed document is read by an optical system in the copy machine body and then conveyed toward a discharge portion (see, Japanese Unexamined Patent Publication No.8-133551, as a similar technique).
Relatedly, it is necessary to previously inform the copy machine body of information about the document size, before reading the document fed from the document tray. Conventionally, there have been arranged a plurality of detection sensors along the document feeding direction in the document tray, and the length of documents have been detected by means of on/off operation of the detection sensors upon placement of documents onto the tray.
However, in the detection means as described above, when the document tray is fed with different sizes of documents in a mixed manner, the detection sensors are caused to constantly detect the maximum size among the mixed documents, causing such a problem that the information of document size is not accurately obtained.
As such, there has been also conventionally proposed a constitution that the detection sensors are arranged on a conveyance path extending from the document tray up to the document reading portion which is opposed to the reading means of the copy machine body and the size of each documents, which are fed from the document tray sheet by sheet, is detected on the conveyance path before the image on the document is read.
However, in such a method that the document size is detected on the conveyance path, as described above, there is required a long conveyance path which is commensurate with the possibly maximum size of document (such as A3 size of document placed in a lengthwise direction), causing a problem that the size of automatic document feeder is increased.
It is therefore an object of the present invention to provide an automatic document feeder which can assuredly detect the document size even by a shortened conveyance path before the image on the document is read, without increasing the size of the feeder itself.
Further, in a conventional automatic document feeder, there has been proposed a feeder capable of reading images on the double sides of the document. This feeder is constituted such that the document fed from a document tray is wound on a large sized conveying roller, conveyed to a document reading portion opposite to a reading means of a copy machine body to be read the front surface thereof in the document reading portion by the reading means of the copy machine body. After that, the document is then reversed by means of a switchback path provided on the downstream side, then the document is conveyed on the periphery of the conveying roller to be read the back surface of thereof and at the same time the document is again reversed by means of a reverse discharge path to be discharged on a discharge tray after page arrangement.
However, such an automatic document feeder as described above should provide both of the switchback path and the reverse discharge path, therefore, there is the problem that the path or feed mechanism becomes complex, resulting in a large sized automatic document feeder. On the other hand, if these two paths are combined into a single path, a radius of curvature of this single path should be made small, resulting in insufficient document conveyance effect.
Moreover, when the document is fed from the switchback path to the conveyance path, the leading edge of the document is aligned using the conveying roller. However, if a distance from the switchback path to a resist position is long as conventionally, since a distance wherein the document slidingly contacts with the periphery of the stopped conveying roller becomes longer, there is a fear that the document cannot be conveyed satisfactorily due to friction with the periphery of the conveying roller.
According to the present invention, the path structure and feeding mechanism are made simple to achieve the minimization of the automatic document feeder itself.
Further, according to the present invention, the radius of curvature of the document discharge path is made small to obtain a sufficient document conveyance effect.
Moreover, according to the present invention, the reversed document conveyed from the switchback path can be reliably aligned without an influence of the periphery friction of the conveying roller.
In the above described Japanese Unexamined Patent Publication No. 8-133551, there has been proposed such a constitution of a book mode for reading the document put on a platen other than a sheet through mode from reading the document being conveyed. In particular, in order to minimize the apparatus, a switchback path used for reading the double sides of the document by reversing the document, and a switchback path for reversing again the document of which double sides have been read to discharge to a discharge tray after page arrangement are further provided between the discharge tray and a platen cover.
However, in a case that a switchback path is provided between the discharge tray and the platen cover as described above, there is a necessity for pulling out the document from a narrow space between the discharge tray and the platen cover when a jam occurs, resulting in difficulty in a jammed document treatment.
According to the present invention, in an apparatus in which the document conveying path, such as a switchback path, is provided between the discharge tray and the platen cover, a document jammed in the document conveying path can be easily treated.
In an automatic document feeder, in order to align the document to be conveyed during the conveying process of the document fed from the document tray, it is necessary to provide a resist roller to feed the document to the reading means of the copy machine body after abutting the leading edge of the document to the resist roller thereby aligning the document. Conventionally, there is proposed an automatic document feeder in which a resist roller is disposed so as to be in pressure contact with a conveying roller, in order to reduce the conveying path from the document tray to the resist roller, so that the document fed from the feeding roller is abutted to the pressure contact portion between the conveying roller and the resist roller to thereby be aligned.
However, with such a constitution as described above, the conveying roller should be stopped at the resist time in order align the document on the conveying roller. Also, the next document cannot be fed to the resist position unless the conveyance of the preceding document is completed. Accordingly, intervals for feeding the document are lengthened, resulting in a long document treatment time.
Accordingly, it is an object of the present invention is to divide the process of document conveyance by means of the conveying roller from the aligning to thereby reduce the document treatment time.
To solve the aforementioned problems, the present invention provides an automatic document feeder comprising:
a document feeding portion for placing documents thereon;
document reading means for reading the documents;
a document discharging portion;
a document conveyance path connecting among the document feeding portion, the document reading portion and the document discharging portion;
a conveying roller, which is capable of forwardly rotating and reversely rotating, for conveying the documents along the document conveyance path;
a document shunting path branched from the document conveyance path;
first detection means for detecting a leading edge and a rear edge of the document; and
second detection means, which is disposed in the document conveyance path on the downstream side of the first detection means, for detecting the leading edge of the document; and
wherein the conveying roller is forwardly rotated to convey the document with the leading edge thereof headed, and, after the rear edge of the document is detected by the first detection means, the conveying roller is reversely rotated to move the rear edge side of the document into the document shunting path, until the leading edge of the document is moved back to a position on the upstream side of the document reading portion.
Further, the present invention provides an automatic document feeder comprising:
a document feeding portion for placing documents thereon;
document reading means for reading the documents;
a document discharging portion;
document conveying means for conveying the documents;
a document conveyance path for conveying the documents from the document feeding portion to the document reading portion or from the document reading portion to the document discharging portion;
a document shunting path branched from the document conveyance path; and
document size detection means for detecting a document size by detecting the leading edge and the rear edge of the document;
wherein the document is conveyed to the document shunting path before being read by the document reading means, then the leading edge of the document is conveyed to the upstream side of the document reading means, and the document size detection means detects the document size while the document is conveyed from the document feeding portion through the document reading means.
According to such a constitution, it is unnecessary to provide a longer conveyance path of documents such as in the conventional, thereby minimizing the size of the document feeder and also detecting accurately the document size.